In inkjet printing, ink droplets are released from an array of nozzles in a print head onto a printing medium, such as paper. The ink bonds to a surface of the printing medium and forms graphics, text, or other images. The ink droplets are released with precision to ensure that the image is accurately formed. Generally, the medium is conveyed under the print head while the droplets are selectively released. The medium's conveyance speed is factored into the droplet release timing.
Print heads typically include a number of ink chambers, also referred to as firing chambers. Each ink chamber is in fluid communication with one of the nozzles in the array and provides the ink to be deposited by that respective print head nozzle. Prior to a droplet release, the ink in the ink chamber is restrained from exiting the nozzle due to capillary forces and/or back pressure acting on the ink within the nozzle passage.
During a droplet release, ink within the ink chamber is forced out of the nozzle by actively increasing the pressure within the chamber. Some print heads use a resistive heater positioned within the chamber to evaporate a small amount of at least one component of the liquid ink. In many cases, a major component of the liquid ink is water, and the resistive heater evaporates the water. The evaporated ink component or components expand to form a gaseous drive bubble within the ink chamber. This expansion exceeds the restraining force enough to expel a single droplet out of the nozzle. Other ink chambers use piezoelectric material membranes to eject ink droplets. The piezoelectric material expands when a voltage is applied to the material, which increases internal pressure of the ink chamber and overcomes the restraining forces enough to expel the droplet.
An ink reservoir may provide ink to the ink chamber. The ink reservoir may be in fluid communication with the chamber with at least one ink feed slot that connects the ink chamber to the ink reservoir. Often, the ink feed slot is formed in a silicon substrate that is bonded to a body of the ink reservoir.